Display, display system, image projection system, and movable object

ABSTRACT

Provided is a head-up display including a liquid-crystal panel including a display screen, a Fresnel lens which is on an opposite side of the liquid-crystal panel from the display screen, a light-diffusion structure between the liquid-crystal panel and the Fresnel lens, a backlight that emits light toward the Fresnel lens, a light-transmissive member between the backlight and the Fresnel lens, and a mirror that forms a virtual image corresponding to an image displayed on the display screen of the liquid-crystal panel, in a target space, where a length of the liquid-crystal panel in a longitudinal direction of the head-up display is longer than a length of the light-transmissive member in the longitudinal direction.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application of U.S. patentapplication Ser. No. 17/666,184, filed Feb. 7, 2022, which is acontinuation of U.S. patent application Ser. No. 17/094,239, filed Nov.10, 2020, now U.S. Pat. No. 11,275,281 issued Mar. 15, 2022, which is acontinuation of U.S. patent application Ser. No. 16/454,218, filed Jun.27, 2019, now U.S. Pat. No. 10,871,686 issued Dec. 22, 2020, whichclaims the benefit of Japanese Patent Application No. 2018-125448, filedJun. 29, 2018. The disclosure of each of the above-mentionedapplications is expressly incorporated herein by reference in itsentirety.

TECHNICAL FIELD

The present disclosure relates to displays, display systems, imageprojection systems, and movable objects. In particular, the presentdisclosure relates to a display for displaying an image, a displaysystem including the display, an image projection system including thedisplay system, and a movable object including the display system.

BACKGROUND ART

JP 2016-31457 A discloses a liquid-crystal display device. Theliquid-crystal display device of JP 2016-31457 A includes aliquid-crystal panel, a transparent member, and a heat sink. Theliquid-crystal panel transmits light from a light source. Thetransparent member covers at least central parts of transmissivesurfaces for light, of the liquid-crystal panel, and is in contact withat least one of the transmissive surfaces. The transparent member hasthermal conductivity higher than that of the liquid-crystal panel andtransmits light. The heat sink is in contact with an edge of thetransparent member and has thermal conductivity higher than that of thetransparent member.

In JP 2016-31457 A, heat generated at the central parts of thetransmissive surfaces of the liquid-crystal panel is transferred to theheat sink through the transparent member. This may contribute toimprovement of heat dissipation. However, according to JP 2016-31457 A,there may be probability of occurrence of interference of light due tocontact between the transparent member (heat-transfer member) and thetransmissive surface of the liquid-crystal panel. Such interference oflight may cause decrease in image quality.

An object would be to propose a display, a display system, an imageprojection system, and a movable object capable of improving heatdissipation and uniformity and additionally improving image quality.

SUMMARY

A display of one aspect according to the present disclosure includes aliquid-crystal panel, a heat-transfer member, and a light-diffusionstructure. The liquid-crystal panel includes a display screen. Theheat-transfer member is light-transmissive. The heat-transfer member ison an opposite side of the liquid-crystal panel from the display screen.The light-diffusion structure is between the liquid-crystal panel andthe heat-transfer member.

A display system of another aspect according to the present disclosureincludes: a display; and a backlight.

An image projection system of another aspect according to the presentdisclosure is used as a head-up display, and includes: the displaysystem; and a projection unit configured to form a virtual imagecorresponding to an image displayed on the display screen of the displaysystem, in a target space.

A movable object of another aspect according to the present disclosureincludes: the display system; and a movable object body where thedisplay system is mounted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic section of a display system including a display ofone embodiment.

FIG. 2 is a conceptual view of a movable object (automobile) where thedisplay system is mounted.

FIG. 3 is a conceptual view of a field of view of a user using thedisplay system.

FIG. 4 is a conceptual view for illustration of the display system.

FIG. 5 is an exploded perspective view of the above display system.

FIG. 6 is a graph showing a time variation of temperatures of thedisplay system and a comparative example.

FIG. 7 is a schematic section of a display system of a first variation.

FIG. 8 is a schematic section of a display system of a second variation.

DETAILED DESCRIPTION 1. Embodiments

1.1 Overview

FIG. 1 is illustration of a display system 110 of one embodiment. Thedisplay system 110 includes a display 20. The display 20 includes aliquid-crystal panel 21, a heat-transfer member 22, and alight-diffusion structure 25 (25 a, 25 b). The liquid-crystal panel 21includes a display screen 21 a. The heat-transfer member 22 islight-transmissive. The heat-transfer member 22 is on an opposite sideof the liquid-crystal panel 21 from the display screen 21 a (i.e., alower surface side in FIG. 1 ). The light-diffusion structure 25 isbetween the liquid-crystal panel 21 and the heat-transfer member 22.

The display 20 includes the heat-transfer member 22 and therefore canhave improved heat-dissipation. Further, the display 20 includes thelight-diffusion structure 25 and therefore can have improved uniformity(uniformity of the display screen 21 a of the liquid-crystal panel 21).Furthermore, the display 20 has the light-diffusion structure 25 betweenthe liquid-crystal panel 21 and the heat-transfer member 22 andtherefore can have improved image quality. In detail, since thelight-diffusion structure 25 is present between the liquid-crystal panel21 and the heat-transfer member 22, interference of light can be reducedin a space between the liquid-crystal panel 21 and the heat-transfermember 22. It is considered the reason is that the light-diffusionstructure 25 prevents close contact between the liquid-crystal panel 21and the heat-transfer member 22 and makes a distance therebetween sothat no interference of light may occur. As described above, the display20 can improve its heat dissipation and its uniformity and furtherimprove its image quality.

1.2 Configuration

Hereinafter, the display 20 and the display system 110 are described inmore detail. In one example, the display system 110 may be mounted on amovable object. FIG. 2 is illustration of an automobile 100 serving asthe movable object. The automobile 100 includes an automotive body 100 aserving as a movable object body, and the display system 110 mounted onthe automotive body 100 a.

In the present embodiment, the display system 110 is used in an imageprojection system 10 shown in FIG. 2 and FIG. 4 . The image projectionsystem 10 is used as a head-up display (HUD) in the automobile 100.

As shown in FIG. 2 , the image projection system 10 is installed in aninterior of the automobile 100 to project an image onto a wind shield101 of the automotive body (movable object body) 100 a of the automobile100 from below. In FIG. 2 , the image projection system 10 is placedinside a dashboard 102 below the wind shield 101. When an image isprojected from the image projection system 10 onto the wind shield 101,the image reflected from the wind shield 101 serving as a reflectivemember may be visually perceived by a user 200 (driver).

The image projection system 10 allows the user 200 to visually perceivea virtual image 310 formed in a target space 400 positioned in front of(outside) the automobile 100 over the wind shield 101. In thisdisclosure, a “virtual image” means an image which is formed by diffusedrays of light caused when light emitted from the image projection system10 is diffused by a reflective member such as the wind shield 101 andappears as if a real object. Therefore, as shown in FIG. 3 , the user200 driving the automobile 100 can see the virtual image 310 which isformed by the image projection system 10 and is overlaid on a real spacespreading in front of the automobile 100. Accordingly, the imageprojection system 10 can display the virtual image 310 indicatingvarious driving assist information such as vehicle speed information,navigation information, pedestrian information, forward vehicleinformation, lane departure information, and vehicle conditioninformation, and can allow the user 200 to visually perceive it. In FIG.3 , the virtual image 310 indicates navigation information exemplifiedby an arrow for lane change. Accordingly, when the user 200 trains hisor her eyes on a space in front of the wind shield 101, the user 200 canvisually obtain the driving assist information by slight movement of aline of his or her sight.

In the image projection system 10, the virtual image 310 created in thetarget space 400 is present within an imaginary plane 501 across anoptical axis 500 of the image projection system 10. In the presentembodiment, the optical axis 500 extends along a road surface 600 infront of the automobile 100 in the target space 400 in front of theautomobile 100. And, the imaginary plane 501 where the virtual image 310is created is almost perpendicular to the road surface 600. For example,when the road surface 600 is in a horizontal plane, the virtual image310 is displayed in a vertical plane. Note that, the imaginary plane 501where the virtual image 310 is created may be inclined relative to theoptical axis 500. An angle of the imaginary plane 501 to the opticalaxis 500 may not be limited particularly.

As shown in FIG. 4 , the image projection system 10 includes the displaysystem 110, a projection unit 120, and a control unit 130.

The display system 110 is configured to display an image. In particular,the display system 110 is used for displaying an image which is formedin the target space 400 as the virtual image 310. As shown in FIG. 1 andFIG. 5 , the display system 110 includes the display 20, a backlight 30,and an optical system 40. Note that, in FIG. 1 and FIG. 5 , only forfacilitating understanding explanations, dimensions of components of thedisplay system 110 are modified accordingly.

As shown in FIG. 1 and FIG. 5 , the display 20 includes theliquid-crystal panel 21, the heat-transfer member 22, a light-diffusionmember 23, and a heat sink 24.

The liquid-crystal panel 21 includes the display screen 21 a. Theliquid-crystal panel 21 transmits light (light from the backlight 30)selectively, thereby forming an image on the display screen 21 a. Theliquid-crystal panel 21 has a rectangular plate shape in whole. Further,the liquid-crystal panel 21 has opposite surfaces (front and rearsurfaces) which are flat. In particular, the liquid-crystal panel 21includes the display screen 21 a in its front surface. The displayscreen 21 a is an area corresponding to part of the front surface of theliquid-crystal panel 21 which transmits light selectively(light-transmissive part). Generally, the liquid-crystal panel 21 mayinclude components including a liquid-crystal layer, a pair of orientedfilms between which the liquid-crystal layer is sandwiched, a pair oftransparent electrodes for applying voltages across the liquid-crystallayer, a color filter for determining colors of individual pixels, and apolarization plate for transmitting a specific component (e.g., ans-component) only. The liquid-crystal panel 21 can have a conventionalstructure, and therefore detailed explanation thereof may be omitted.

The heat-transfer member 22 is light-transmissive. The heat-transfermember 22 is on an opposite side of the liquid-crystal panel 21 from thedisplay screen 21 a. Purposes of providing the heat-transfer member 22may include improvement of heat dissipation of the display 20.Especially, the heat-transfer member 22 may reduce increase intemperature of the liquid-crystal panel 21. The heat-transfer member 22has thermal conductivity higher than thermal conductivity of theliquid-crystal panel 21. Examples of material of the heat-transfermember 22 may include normal glass, clear glass, sapphire glass, and thelike. The heat-transfer member 22 has a rectangular plate shape inwhole, similarly to the liquid-crystal panel 21. Additionally, theheat-transfer member 22 has opposite surfaces (front and rear surfaces)which are flat. In the present embodiment, the heat-transfer member 22has the same size as the liquid-crystal panel 21. However, it is notnecessary that the heat-transfer member 22 has the same size as theliquid-crystal panel 21. When the heat-transfer member 22 is larger thanthe liquid-crystal panel 21, it is sufficient that part of theheat-transfer member 22 which overlaps with the liquid-crystal panel 21is light-transmissive.

The light-diffusion member 23 is present between the liquid-crystalpanel 21 and the heat-transfer member 22. Purposes of providing thelight-diffusion member 23 may include improvement of uniformity(uniformity of the display screen 21 a of the liquid-crystal panel 21).The light-diffusion member 23 has a rectangular plate shape. Thelight-diffusion member 23 is light-transmissive. Examples of mainmaterial of the light-diffusion member 23 may include glass and resin.Note that, it is preferable that the light-diffusion member 23 does nothave thermally-insulating properties. The light-diffusion member 23 isthinner than the heat-transfer member 22. Especially, in FIG. 1 , thelight-diffusion member 23 appears to be slightly thinner than theheat-transfer member 22. Actually, the heat-transfer member 22 has athickness of about 2 mm but the light-diffusion member 23 has athickness of about 100 μm. Additionally, it is preferable that thelight-diffusion member 23 has a size enough to cover thelight-transmissive part of the liquid-crystal panel 21.

The light-diffusion member 23 includes two light-diffusion structures 25(25 a and 25 b). One light-diffusion structure 25 a is formed in anentire surface of the light-diffusion member 23 facing or closer to theliquid-crystal panel 21 (an upper surface in FIG. 1 ) and the otherlight-diffusion structure 25 b is formed in an entire surface of thelight-diffusion member 23 facing or closer to the heat-transfer member22 (a lower surface in FIG. 1 ). The light-diffusion structures 25 a and25 b have the same structure. In the present embodiment, thelight-diffusion structures 25 are provided to both of the surface of thelight-diffusion member 23 facing the liquid-crystal panel 21 (the uppersurface in FIG. 1 ) and the surface of the light-diffusion member 23facing the heat-transfer member 22 (the lower surface in FIG. 1 ). Thelight-diffusion structures 25 may be formed by mechanically processingsurfaces of a substrate serving as a base of the light-diffusion member23. Alternatively, the light-diffusion structures 25 may be formed byapplying binders in which fine particles are dispersed onto the surfacesof the substrate and drying them. In this case, the light-diffusionstructures 25 may include a plurality of fine particles. The structureof the light-diffusion structure 25 itself may be conventional, andtherefore no detail explanation thereof is given. However, variousparameters of the structure of the light-diffusion member 23 may beselected as follows. In an example, the light-diffusion member 23 maypreferably have a transmittance equal to or higher than 70%. Thus, thelighting performance of the display 20 can be improved. Especially, thelighting performance of the display 20 may easily satisfy specificationsrequired for head-up displays. Note that, the transmittance may bedetermined by a method defined in “Plastics—Determination of totalluminous transmittance and reflectance” (JIS K 7375). Thelight-diffusion member 23 may preferably have haze equal to or largerthan 30%. The light-diffusion member 23 may preferably have haze equalto or smaller than 90%. Thus, the lighting performance of the display 20can be improved. Especially, the lighting performance of the display 20may easily satisfy specifications required for head-up displays. Notethat, the haze may be determined by a method defined in“Plastics—Determination of haze for transparent materials” (JIS K 7136).The light-diffusion member 23 may preferably have a thickness equal toor smaller than 300 μm. Thus, the heat dissipation of the display 20 canbe improved. Note that, the thickness may be determined by a methoddefined in “Plastics—Film and sheeting—Determination of thickness” (JISK 7130). In a case where the light-diffusion member 23 includes alight-diffusion structure 25 including a plurality of fine particles, anaverage particle size of the fine particles contained in thelight-diffusion structure 25 (surface average particle size) may bepreferably equal to or smaller than 20 μm. Thus, the heat dissipation ofthe display 20 can be improved. Note that, the average particle size maybe determined by a method defined in “Particle size analysis—Imageanalysis methods—Part 1: Static image analysis methods” (JIS Z 8827-1).

Purposes of providing the heat sink 24 may include improvement of heatdissipation of the display 20. The heat sink 24 is thermally coupledwith the heat-transfer member 22. The heat sink 24 has a thermalconductivity higher than a thermal conductivity of the heat-transfermember 22. The heat sink 24 may be made of aluminum, for example. Theheat sink 24 includes a body part 241 and a plurality of fins 242. Thebody part 241 has a hollow rectangular prism shape. The body part 241includes a first accommodation part 241 a and a second accommodationpart 241 b which are coupled to each other. The first accommodation part241 a serves as a space for accommodating the heat-transfer member 22.The second accommodation part 241 b is formed in a bottom surface of thefirst accommodation part 241 a. The second accommodation part 241 b issmaller than the first accommodation part 241 a. Therefore, theheat-transfer member 22 may be supported on a periphery of the bottomsurface of the first accommodation part 241 a (a periphery of the secondaccommodation part 241 b). As shown in FIG. 1 , the second accommodationpart 241 b serves as a space for accommodating the backlight 30 and theoptical system 40. The plurality of fins 242 have rectangular plateshapes. The plurality of fins 242 protrude from an outer surface of thebody part 241.

The backlight 30 is a light source device configured to emit rays oflight for forming an image on the display screen 21 a of theliquid-crystal panel 21. The backlight 30 is a planer light source.Examples of light sources used in the backlight 30 may include solidlight emitting devices such as light emitting diodes and laser diodes.Note that, the backlight 30 may have a conventional configuration, andtherefore no detailed explanation is given.

The optical system 40 is placed between the display 20 and the backlight30. The optical to system 40 is used for converting light from thebacklight 30 into light with desired properties. In the presentembodiment, the optical system 40 is used for making light from thebacklight 30 diverge in a desired direction (e.g., a directionperpendicular to the thickness of the liquid-crystal panel 21). Theoptical system 40 includes a Fresnel lens 41 and a prism sheet 42. TheFresnel lens 41 has a rectangular plate shape. The Fresnel lens 41 ismade of light-transmissive material (e.g., glass or resin). The Fresnellens 41 is situated facing the backlight 30. The Fresnel lens 41functions as a diverging lens for allowing light from the backlight 30to diverge in a desired direction. The prism sheet 42 has a rectangularplate shape. The prism sheet 42 is made of light-transmissive material(e.g., glass or resin). The prism sheet 42 is placed between the Fresnellens 41 and the backlight 30. The prism sheet 42 functions as an opticaldevice having a polarization function for directing light from thebacklight 30 toward the Fresnel lens 41.

In the display 20, as shown in FIG. 1 , the backlight 30 and the opticalsystem 40 are accommodated in the second accommodation part 241 b of theheat sink 24 of the display 20. Further, as shown in FIG. 1 , theheat-transfer member 22 is accommodated in the first accommodation part241 a of the heat sink 24. The liquid-crystal panel 21 is placed on theheat-transfer member 22 with the light-diffusion member 23 in-between.Accordingly, the light-diffusion member 23 is in contact with both ofthe liquid-crystal panel 21 and the heat-transfer member 22, therebythermally interconnecting them. Therefore, heat generated in theliquid-crystal panel 21 may be transferred to the heat-transfer member22 through the light-diffusion member 23. Based on common generalknowledge, there may be concern that presence of the light-diffusionmember 23 between the liquid-crystal panel 21 and the heat-transfermember 22 causes decrease in heat transfer efficiency. In view of this,an experiment for confirming whether or not the light-diffusion member23 causes decrease in the heat transfer efficiency was conducted. FIG. 6shows results of this experiment. FIG. 6 shows a time variation oftemperature of the liquid-crystal panel 21, and G10 corresponds to thedisplay 20. In contrast, G20 corresponds to a display 20 devoid of thelight-diffusion member 23. As apparent from FIG. 6 , it was notconfirmed that decrease in the heat transfer efficiency was caused bypresence of the light-diffusion member 23 between the liquid-crystalpanel 21 and the heat-transfer member 22. In other words, it wasconfirmed that presence of the light-diffusion member 23 between theliquid-crystal panel 21 and the heat-transfer member 22 did not givelarge influences on the heat transfer efficiency.

The projection unit 120 is used for forming the virtual image 310corresponding to the image (the image displayed on the display screen 21a of the display system 110) in the target space 400. Stateddifferently, the projection unit 120 is configured to form, in thetarget space 400, the virtual image 310 corresponding to the imagedisplayed on the display screen 21 a of the liquid-crystal panel 21 ofthe display 20 (the image displayed on the display screen 21 a of thedisplay system 110). The projection unit 120 is configured to form thevirtual image 310 in the target space 400 by reflecting rays of lightconstituting the image presented by the display system 110 toward areflective member (the wind shield) 101 to project the image onto thereflective member 101. As shown in FIG. 4 , the projection unit 120includes a first optical member 121 and a second optical member 122. Inother words, the projection unit 120 is an optical system constituted bythe first optical member 121 and the second optical member 122.

The projection unit 120 forms the virtual image 310 corresponding to theimage (the image formed on the display screen 21 a of the liquid-crystalpanel 21) in the target space 400, by use of rays of light passingthrough the liquid-crystal panel 21 of the display system 110. As shownin FIG. 4 , the projection unit 120 includes the first optical member121 and the second optical member 122. The first optical member 121 is amirror for reflecting light from the display system 110 toward thesecond optical member 122. The second optical member 122 is a mirror forreflecting light from the first optical member 121 toward the windshield 101. Accordingly, the projection unit 120 projects the imageformed on the display screen 21 a of the liquid-crystal panel 21 ontothe wind shield 101 by use of the first optical member 121 and thesecond optical member 122, thereby forming the virtual image 310 in thetarget space 400.

The control unit 130 is configured to control the liquid-crystal panel21 and the backlight 30 of the display system 110. The control unit 130controls the liquid-crystal panel 21 and the backlight 30 based on animage signal given, thereby forming an image on the display screen 21 aof the liquid-crystal panel 21. The control unit 130 may be implementedby a conventional control circuit for liquid-crystal displays.

1.3 Conclusion

In the display 20 as described above, the light-diffusion structure 25is present between the liquid-crystal panel 21 and the heat-transfermember 22 and therefore the image quality can be improved. In detail,since the light-diffusion structure 25 is present between theliquid-crystal panel 21 and the heat-transfer member 22, interference oflight can be reduced in a space between the liquid-crystal panel 21 andthe heat-transfer member 22. It is considered the reason is that thelight-diffusion structure 25 prevents close contact between theliquid-crystal panel 21 and the heat-transfer member 22 and makes adistance therebetween so that no interference of light may occur. Asdescribed above, the display 20 can improve its heat dissipation and itsuniformity and further improve its image quality. In addition, thedisplay 20 includes the light-diffusion member 23 between theliquid-crystal panel 21 and the heat-transfer member 22, but it isconsidered that there is no substantial influence on heat transferbetween the liquid-crystal panel 21 and the heat-transfer member 22.Therefore, the uniformity and the image quality can be improved withoutlosing the heat dissipation.

2. Variations

Embodiments of the present disclosure are not limited to the aboveembodiment. The above embodiment may be modified in various ways inaccordance with design or the like as it can achieve the object of thepresent disclosure. Hereinafter, variations of the above embodiment arelisted.

2.1 First Variation

FIG. 7 is illustration of a display system 110A of a first variation.The display system 110A includes a display 20A, a backlight 30, and anoptical system 40. Note that, in FIG. 7 , only for facilitatingunderstanding explanations, dimensions of components of the displaysystem 110A are modified accordingly.

The display 20A includes a liquid-crystal panel 21A, a heat-transfermember 22, and a heat sink 24. The display 20A is different from thedisplay 20 in that the display 20A does not include the light-diffusionmember 23. Instead, the liquid-crystal panel 21A includes alight-diffusion structure 25 (25 c). In more detail, the light-diffusionstructure 25 c is provided to an opposite surface of the liquid-crystalpanel 21A from the display screen 21 a (a lower surface in FIG. 7 ). Thelight-diffusion structure 25 c may preferably extend to cover entirelight-transmissive part of the liquid-crystal panel 21A. Thelight-diffusion structures 25 c may be formed by mechanically processinga surface of the liquid-crystal panel 21A or by applying a binder inwhich fine particles are dispersed onto the liquid-crystal panel 21A.The structure of the light-diffusion structure 25 c itself may beconventional, and therefore no detail explanation thereof is given.

In the display 20A, the liquid-crystal panel 21A is placed on theheat-transfer member 22 such that the light-diffusion structure 25 c isdirected to the heat-transfer member 22. Thus, the light-diffusionstructure 25 c is in contact with the heat-transfer member 22.Accordingly, the liquid-crystal panel 21A and the heat-transfer member22 are thermally coupled with each other. Heat generated in theliquid-crystal panel 21A is transferred to the heat-transfer member 22directly.

The display 20A includes the heat-transfer member 22 and thelight-diffusion structure 25 c and therefore the heat dissipation andthe uniformity can be improved. Further, in the display 20A, thelight-diffusion structure 25 c is positioned between the liquid-crystalpanel 21A and the heat-transfer member 22 and therefore the imagequality can be improved. In particular, the display 20A does not requirean additional part such as the light-diffusion member 23 to provide thelight-diffusion structure 25 c. Hence, it can be easy to provide thelight-diffusion structure 25 c. Additionally, in the display 20A, heatgenerated in the liquid-crystal panel 21A can be transferred to theheat-transfer member 22 directly. Consequently, the heat dissipation canbe improved.

2.2 Second Variation

FIG. 8 is illustration of a display system 110B of a second variation.The display system 110B includes a display 20B, a backlight 30, and anoptical system 40. Note that, in FIG. 8 , only for facilitatingunderstanding explanations, dimensions of components of the displaysystem 110B are modified accordingly.

The display 20B includes a liquid-crystal panel 21, a heat-transfermember 22B, and a heat sink 24. The display 20B is different from thedisplay 20 in that the display 20B does not include the light-diffusionmember 23. Instead, the heat-transfer member 22B includes alight-diffusion structure 25 (25 d). In more detail, the light-diffusionstructure 25 d is provided to a surface of the heat-transfer member 22Bfacing the liquid-crystal panel 21 (an upper surface in FIG. 8 ). Thelight-diffusion structure 25 d may preferably extend to cover entirelight-transmissive part of the liquid-crystal panel 21. Thelight-diffusion structures 25 d may be formed by mechanically processinga surface of the heat-transfer member 22B or by applying a binder inwhich fine particles are dispersed onto the heat-transfer member 22B.The structure of the light-diffusion structure 25 d itself may beconventional, and therefore no detail explanation thereof is given.

In the display 20B, the heat-transfer member 22B is placed on the heatsink 24 so that the light-diffusion structure 25 d is opposite from thebacklight 30. The liquid-crystal panel 21 is placed on thelight-diffusion structure 25 d of the heat-transfer member 22. Thus, thelight-diffusion structure 25 d is in contact with the liquid-crystalpanel 21. Accordingly, the liquid-crystal panel 21 and the heat-transfermember 22B are thermally coupled with each other. Heat generated in theliquid-crystal panel 21 is transferred to the heat-transfer member 22Bdirectly.

The display 20B includes the heat-transfer member 22B and thelight-diffusion structure 25 d and therefore the heat dissipation andthe uniformity can be improved. Further, in the display 20B, thelight-diffusion structure 25 d is positioned between the liquid-crystalpanel 21 and the heat-transfer member 22B and therefore the imagequality can be improved. In particular, the display 20B does not requirean additional part such as the light-diffusion member 23 to provide thelight-diffusion structure 25 d. Hence, it can be easy to provide thelight-diffusion structure 25 d. Additionally, in the display 20B, heatgenerated in the liquid-crystal panel 21 can be transferred to theheat-transfer member 22B directly. Consequently, the heat dissipationcan be improved.

2.3 Other Variations

For example, in the display 20, the light-diffusion member 23 does notnecessarily include the light-diffusion structure 25 (25 a, 25 b)provided to each of the surface facing the liquid-crystal panel 21 andthe surface facing the heat-transfer member 22. Stated differently, thelight-diffusion structure 25 may be provided to the surface of thelight-diffusion member 23 facing the liquid-crystal panel 21 only. Inthis case, the surface of the light-diffusion member 23 facing theheat-transfer member 22 may be flat. Or, the light-diffusion structure25 may be provided to the surface of the light-diffusion member 23facing the heat-transfer member 22 only. In this case, the surface ofthe light-diffusion member 23 facing the liquid-crystal panel 21 may beflat. However, it is preferable that the surface of the light-diffusionmember 23 facing the liquid-crystal panel 21 is subjected to adherencesuppression treatment. In other words, the light-diffusion member 23preferably includes an adherence suppression structure at the surfacethereof facing the liquid-crystal panel 21. The adherence suppressionstructure can be provided by roughing the surface of the light-diffusionmember 23 facing the liquid-crystal panel 21 or coating it with resin inwhich fine particles are dispersed. Note that, the light-diffusionstructure 25 may also serve as an adherence suppression structure.

For example, the optical system 40 does not require the prism sheet 42provided that an amount of light outputted from the backlight 30 andstriking the Fresnel lens 41 falls within an allowable range. Theoptical system 40 may include one or more additional Fresnel lensesbetween the Fresnel lens 41 and the backlight 30. Note that, the shapeof the Fresnel lens 41 may not be limited particularly. The opticalsystem 40 may not necessarily include the Fresnel lens 41. Use of theoptical system 40 may not be limited to divergence of light. Forexample, the optical system 40 may be used for convergence of light fromthe backlight 30. In one example, the optical system 40 may include atleast one of a condenser lens and a field lens. The configuration of theoptical system 40 may be modified appropriately in accordance withproperties of light from the backlight 30. Or, the display system 110may not include the optical system 40.

For example, outer shapes of components of the display (20; 20A; 20B)may not be limited particularly. In one example, the outer shapes of theliquid-crystal panel (21; 21A), the heat-transfer member (22; 22B), andthe light-diffusion member 23 may not be necessarily rectangular, butmay be circular or polygonal such as square.

For example, regarding the projection unit 120, shapes of the firstoptical member 121 and the second optical member 122 can be modified.For example, the shapes of the first optical member 121 and the secondoptical member 122 can have appropriate shapes in accordance with thedisplay screen 21 a.

For example, the image projection system 10 may not be limited to aconfiguration of forming the virtual image 310 in the target space 400set in front of the automobile 100 in relation to a moving directionthereof. However, the image projection system 10 may form the virtualimage 310 beside, behind, or over the automobile 100 in relation to themoving direction thereof, for example. The projection unit 120 mayinclude a relay optical system for forming an intermediate image but maynot include such a relay optical system.

For example, the image projection system 10 may apply to not only ahead-up display used in the automobile 100 but also a movable objectother than the automobile 100, such as a bicycle, a train, an aircraft,a construction machine, a boat and a ship. The image projection system10 may not be limited to being used in movable objects but may be usedin amusement facilities.

3. Aspects

As obviously understood from the embodiments and variations, the presentdisclosure contains the following aspects. In the following, thereference signs in parentheses are introduced in order to clearlyindicate relation between the aspects and the embodiment and variations.

A first aspect is a display (20; 20A; 20B) including: a liquid-crystalpanel (21; 21A); a heat-transfer member (22; 22B); and a light-diffusionstructure (25). The liquid-crystal panel (21; 21A) includes a displayscreen (21 a). The heat-transfer member (22; 22B) is light-transmissiveand is on an opposite side of the liquid-crystal panel (21; 21A) fromthe display screen (21 a). The light-diffusion structure (25) is betweenthe liquid-crystal panel (21; 21A) and the heat-transfer member (22;22B). Accordingly, the first aspect is capable of improving heatdissipation and uniformity and additionally improving image quality.

A second aspect is a display (20) which would be realized in combinationwith the first aspect. In the second aspect, the display (20) furtherincludes a light-diffusion member (23) between the liquid-crystal panel(21) and the heat-transfer member (22). The light-diffusion member (23)includes the light-diffusion structure (25 a, 25 b). According to thesecond aspect, it can be easy to provide the light-diffusion structure(25 a, 25 b).

A third aspect is a display (20) which would be realized in combinationwith the second aspect. In the third aspect, the light-diffusionstructure (25 a) is provided to a surface of the light-diffusion member(23) facing the liquid-crystal panel (21). Accordingly, the third aspectis capable of improving heat dissipation and uniformity and additionallyimproving image quality.

A fourth aspect is a display (20) which would be realized in combinationwith the second aspect. In the fourth aspect, the light-diffusionstructure (25 b) is provided to a surface of the light-diffusion member(23) facing the heat-transfer member (22). Accordingly, the fourthaspect is capable of improving heat dissipation and uniformity andadditionally improving image quality.

A fifth aspect is a display (20) which would be realized in combinationwith the fourth aspect. In the fifth aspect, the light-diffusion member(23) includes an adherence suppression structure at a surface thereoffacing the liquid-crystal panel (21). Accordingly, the fifth aspect iscapable of improving heat dissipation and uniformity and additionallyimproving image quality.

A sixth aspect is a display (20) which would be realized in combinationwith the second aspect. In the sixth aspect, the light-diffusionstructure (25 a, 25 b) is provided to each of a surface of thelight-diffusion member (23) facing the liquid-crystal panel (21) and asurface of the light-diffusion member (23) facing the heat-transfermember (22). Accordingly, the sixth aspect is capable of improving heatdissipation and uniformity and additionally improving image quality.

A seventh aspect is a display (20) which would be realized incombination with any one of the second to sixth aspects. In the seventhaspect, the heat-transfer member (22) and the light-diffusion member(23) have plate shapes. The light-diffusion member (23) is thinner thanthe heat-transfer member (22). Accordingly, the seventh aspect iscapable of further improving heat dissipation.

An eighth aspect is a display (20) which would be realized incombination with any one of the second to seventh aspects. In the eighthaspect, the light-diffusion member (23) has a transmittance equal to orlarger than 70%. The light-diffusion member (23) has haze equal to orlarger than 30% and equal to or smaller than 90%. Accordingly, theeighth aspect allows a lighting performance of the display (20) toeasily satisfy requirements for head-up displays.

A ninth aspect is a display (20) which would be realized in combinationwith the seventh or eighth aspect. In the ninth aspect, thelight-diffusion member (23) has a thickness equal to or smaller than 300μm. Accordingly, the ninth aspect is capable of improving heatdissipation.

A tenth aspect is a display (20; 20A; 20B) which would be realized incombination with any one of the first to eighth aspects. In the tenthaspect, the light-diffusion structure (25) includes a plurality of fineparticles. An average particle size of the plurality of fine particlesis equal to or smaller than 20 μm. Accordingly, the tenth aspect iscapable of improving heat dissipation.

An eleventh aspect is a display (20) which would be realized incombination with the seventh or eighth aspect. In the eleventh aspect,the light-diffusion member (23) has a thickness equal to or smaller than300 μm. The light-diffusion structure (25) includes a plurality of fineparticles. An average particle size of the plurality of fine particlesis equal to or smaller than 20 μm. Accordingly, the eleventh aspect iscapable of improving heat dissipation.

A twelfth aspect is a display (20A) which would be realized incombination with any one of the first to eleventh aspects. In thetwelfth aspect, the light-diffusion structure (25 c) is provided to asurface of the liquid-crystal panel (21A) opposite from the displayscreen (21 a). According to the twelfth aspect, it can be easy toprovide the light-diffusion structure (25 c).

A thirteenth aspect is a display (20A) which would be realized incombination with the twelfth aspect. In the thirteenth aspect, thelight-diffusion structure (25 c) is in contact with the heat-transfermember (22). Accordingly, the thirteenth aspect is capable of improvingheat dissipation.

A fourteenth aspect is a display (20B) which would be realized incombination with any one of the first to thirteenth aspects. In thefourteenth aspect, the light-diffusion structure (25 d) is provided to asurface of the heat-transfer member (22B) facing the liquid-crystalpanel (21). According to the fourteenth aspect, it can be easy toprovide the light-diffusion structure (25 d).

A fifteenth aspect is a display (20B) which would be realized incombination with the fourteenth aspect. In the fifteenth aspect, thelight-diffusion structure (25 d) is in contact with the liquid-crystalpanel (21). Accordingly, the fifteenth aspect is capable of improvingheat dissipation.

A sixteenth aspect is a display (20; 20A; 20B) which would be realizedin combination with any one of the first to fifteenth aspects. In thesixteenth aspect, the display (20; 20A; 20B) further includes a heatsink (24) thermally coupled with the heat-transfer member (22; 22B).Accordingly, the sixteenth aspect is capable of further improving heatdissipation.

A seventeenth aspect is a display (20; 20A; 20B) which would be realizedin combination with the sixteenth aspect. In the seventeenth aspect, theheat-transfer member (22) has a thermal-conductivity higher than athermal-conductivity of the liquid-crystal panel (21). Accordingly, theseventeenth aspect is capable of improving heat dissipation.

An eighteenth aspect is a display system (110; 110A; 110B) including: adisplay (20; 20A; 20B) according to any one of the first to seventeenthaspects; and a backlight (30). Accordingly, the eighteenth aspect iscapable of improving heat dissipation and uniformity and additionallyimproving image quality.

A nineteenth aspect is an image projection system (10) used as a head-updisplay, including: the display system (110; 110A; 110B) according tothe eighteenth aspect; and a projection unit (120). The projection unit(120) is configured to form a virtual image (310) corresponding to animage displayed on the display screen (21 a) of the display system (110;110A; 110B), in a target space (400). Accordingly, the nineteenth aspectis capable of improving heat dissipation and uniformity and additionallyimproving image quality.

A twentieth aspect is a movable object (100) including: the displaysystem (110; 110A; 110B) according to the eighteenth aspect; and amovable object body (100 a) where the display system (110; 110A; 110B)is mounted. Accordingly, the twentieth aspect is capable of improvingheat dissipation and uniformity and additionally improving imagequality.

While various embodiments have been described herein above, it is to beappreciated that various changes in form and detail may be made withoutdeparting from the spirit and scope of the present disclosure presentlyor hereafter claimed.

The entire contents of Japanese Patent Application No. 2018-125448mentioned above are incorporated by reference.

The invention claimed is:
 1. A head-up display comprising: aliquid-crystal panel including a display screen; a Fresnel lens which ison an opposite side of the liquid-crystal panel from the display screen;a light-diffusion structure between the liquid-crystal panel and theFresnel lens; a backlight that emits light toward the Fresnel lens; alight-transmissive member between the backlight and the Fresnel lens;and a mirror that forms a virtual image corresponding to an imagedisplayed on the display screen of the liquid-crystal panel, in a targetspace, wherein a length of the liquid-crystal panel in a longitudinaldirection of the head-up display is longer than a length of thelight-transmissive member in the longitudinal direction.
 2. The head-updisplay according to claim 1, wherein a length of the liquid-crystalpanel in the longitudinal direction is longer than a length of theFresnel lens in the longitudinal direction.
 3. The head-up displayaccording to claim 1, further comprising a body part accommodating thelight-diffusion structure, the backlight and the Fresnel lens.
 4. Thehead-up display according to claim 3, wherein the body part has aplurality of plate-shaped fins protruding from an outer surface of theheat sink in a direction intersecting a direction in which thelight-diffusion structure and the Fresnel lens are arranged.
 5. Thehead-up display according to claim 3, wherein the body part is made ofaluminum.
 6. The head-up display according to claim 1, wherein lightemitted from the backlight diverges in a direction toward the Fresnellens.
 7. The head-up display according to claim 1, wherein light emittedfrom the backlight converges in a direction toward the Fresnel lens. 8.The head-up display according to claim 1, wherein the light-diffusionstructure is provided to a surface of a light-diffusion member facingthe liquid-crystal panel.
 9. The head-up display according to claim 1,wherein the light-diffusion structure is provided to a surface of alight-diffusion member facing the Fresnel lens.
 10. The head-up displayaccording to claim 1, wherein the light-diffusion structure is providedto each of a surface of a light-diffusion member facing theliquid-crystal panel and a surface of the light-diffusion member facingthe Fresnel lens.
 11. The head-up display according to claim 1, whereinthe light-diffusion structure is included in a light-diffusion member;and the light-diffusion member is made of glass or resin.
 12. Thehead-up display according to claim 1, wherein the light-diffusionstructure is included in a light-diffusion member; and thelight-diffusion member is made of resin in which fine particles aredispersed.
 13. The head-up display according to claim 1, wherein thebacklight includes light emitting diodes or laser diodes.
 14. Thehead-up display according to claim 1, wherein an uneven surface of theFresnel lens is on the backlight side.